1. Field of the Invention
The present invention relates to a light-emitting device and an optical integrated device, and more particularly to a light-emitting device and an optical integrated device having superior characteristics which enable an optical picking-up function for realizing a high level of space resolution to be achieved by a small, light-weight, less power-consuming and highly ambience-resistant device fabricated in a monolithic process.
2. Description of the Prior Art
As an example of the prior art, an optical pickup device matching optical disk type recording media, which now constitutes the mainstream of such elements, will be described. FIG. 1 illustrates the basic configuration of a currently mainstream optical pickup. The configuration and operation of this type pickup, which is extensively used by those engaged in the art, are described in, for instance, Applied Physics, Vol. 67, No. 9 (1998), pp. 1035–1040 (in Japanese). A probe light emitted from a semiconductor laser 101, traveling via a diffraction grating 102, is folded 90 degrees by a half mirror 103, and is condensed by an objective lens 104 to irradiate the upper surface of an optical disk 105. The incident probe light is reflected and scattered by a pattern drawn on the surface of the optical disk 105. Lights reflected or scattered backward are condensed by the objective lens 104, the condensed light is transmitted straight by the half mirror 103, and its intensity is detected by a photodiode 106 arranged behind. The semiconductor laser 101, which serves as the light source, uses a wavelength of 780 nm (for a compact disk (CD) or a Mini Disk (MD)) or 635–650 nm (for a digital versatile disk (DVD)), depending on the type of the optical disk 105. Regions of two different reflection factors are written on the surface of the optical disk 105 with a precision of the μm level. Relative intensities of reflected lights resulting from the irradiation with the probe light are detected and translated into digital signals. A space resolution d with respect to the reading of write patterns can be expressed in the following equation, wherein λ is the wavelength of the probe light and NA, the numerical aperture of the objective lens:d=0.7λ/NA  (1)
The shorter the wavelength λ of the probe light and the greater the numerical aperture NA of the objective lens, the higher the space resolution, i.e. the denser the recording by the memory. The NA of optical pickup device commercially available today is about 0.45 for CDs and 0.6 for DVDs. The above-described optical pickup device is configured by assembling individual basic components including the semiconductor laser 101, diffraction grating 102, half mirror 103, objective lens 104 and photodiode 106.
However, there are limits to reductions in size, weight and power consumption of the above-described optical pickup device according to the prior art, because basically it is fabricated in a process of assembling discrete components. Further, in order to enhance the space resolution, an indispensable requirement for increasing the recording density, it is necessary to increase the aperture rate of the objective lens or to shorten the wavelength of the semiconductor laser, which is the light source. The former would inevitably result in a greater hardware size, while the latter, as it requires development back to the stage of growth of new type single semiconductor crystals excelling in material composition, would be enormously time-consuming and expensive. These are essential impediments to functional upgrading.